class_docstr: :param trace_dist: a TracePosterior instance representing a Monte Carlo posterior
  
  Marginal histogram distribution.
  Turns a TracePosterior object into a Distribution
  over the return values of the TracePosterior's model.
code: def mean(self):
      samples = torch.stack(list(self._dist_and_values()[1].values()))
      return self._weighted_mean(samples)
  
imports: import collections
  import functools
  import queue
  import torch
  import pyro.distributions
  import pyro.poutine
  from pyro.infer.abstract_infer import TracePosterior
  from pyro.poutine.runtime import NonlocalExit
label_desc: Use image node_id 8 for calling the HashingMarginal obj's underlying member method code with example usage: obj.mean() and returns: self